Conceptually adiabatic mass exchanger is simply the combination of a heat exchanger plus a mass exchanger. However effective mass exchange has very exacting requirements, relating to liquid distribution, mixing of bulk flows, and achievement of vapor-liquid contact surface. Most straightforward combinations of known heat exchangers with known mass exchangers cause a marked degradation in the expected mass exchange.
Nonetheless, there is a substantial benefit to identifying and implementing those few combinations which do yield effective diabatic mass exchange, for the processes using them can achieve major efficiency gains and size reductions.
Diabatic fractionators have been referred to as "reflux heat exchangers", "reflux condensers", or as "dephlegmators." Prior art embodiments have generally been the plate fin type, as disclosed in U.S. Pat. Nos. 3,508,412; 3,625,017; and 5,316,628. Note also U.S. Pat. No. 5,410,885.
One special case of diabatic mass exchange is found in absorption heat pumps. Prior art examples of diabatic mass exchangers in absorption heat pumps are found in U.S. Pat. Nos. 4,127,009; 4,688,399; 5,282,507; 5,367,884; and 5,339,654.
Two cases can be distinguished, according to whether the less volatile component (the sorbent) is non-volatile, in which case the vapor is single component, or the sorbent is volatile, i.e. the vapor is multicomponent. Countercurrent mass exchange becomes very important in most vapor-liquid contact operations with volatile sorbents, and especially so in GAX absorption cycles.
Whereas most prior art disclosed embodiments of diabatic mass exchangers have been the plate fin type, some have been shell and tube (U.S. Pat. No. 5,255,528), and some have been helically coiled tubing.
The various prior art embodiments generally have one or more shortcomings: insufficient liquid distribution; insufficient bulk mixing of liquid and/or of vapor; excessive fluid inventory; costly and difficult construction practices; excessive pressure drop; and/or not suitable for countercurrent vapor-liquid contact. What is needed, and among the objects of this invention, are process and apparatus for diabatic mass exchange which efficiently establishes and maintains good liquid distribution and wetting; which achieves good vapor-liquid mass transfer and low pressure drop coupled with effective heat exchange; reduced fluid inventory; and which is easily manufacturable from readily available components